As it happens, personally I'm pretty indifferent to cake, but I do love toolmaking, so everyone's a winner...

Brief

I wanted this to be an enjoyably functioning tool, so that cake cutting and serving became more ritualistic than it is when just using an inadequate and/or unsatisfactory knife in a drawer as an afterthought.

In addition, to make it more fun I restricted this build thus:

the raw materials had to be either recycled or foraged

the finished product should not be finished too much, so that it would be possible to see how it had been made

I time boxed the build to a single working day (well, 7.5 hours in total) to make decision making more challenging.

I extended this to a second time boxed one-day build by making a presentation box. That's for another post though...

Making the blade (about 3 hours)

Choice of steel was important. A slice needs to be super thin, flexible, stainless and be able to hold a keen edge. After scouring my shed for metal objects, I eventually realised that a saw blade would be perfect for this. Conveniently I had just replaced my handsaw which was 10 years old and not as keen as it used to be.

Bingo - steel found!

So, fare thee well, old trusty saw. A new life awaits thee...

The outline of the cake slice blade was drawn out on the old saw blade with a trusty Sharpie

This was then hacked out roughly using the angle grinder with a diamond tipped cutting blade. Sparks flew of course...

Here it is, half way through initial cutting out

Once the shape was cut out rough, it was ground down to the final shape on an inverted belt sander with a rough grit belt (80 grit, in fact)

And once cut to shape it was ground thinner using progressively finer grit (180 was the finest I had).
Eventually a nice whippy blade was made. In this photo, it is ground, but not polished

I then merely had to bend the blade twice to get the required final shape. This should be done on an anvil by heating the blade to red heat in a forge, but given my time contraint, I thought I'd use a blowtorch instead

Sadly, that failed to heat evenly and the blade snapped when trying to fold it.

To stick to the time box restraint, I decided to just weld it back together! So out came this baby...

And of course, the great thing about welding is that you get to dress up like a serial killer.
Leatherface, eat your heart out...

Grips helped keep the blade in position

After welding it back together, the blade looks pretty rough. Here, Betty pug is looking baffled. That is nothing to do with the blade. She always looks baffled (and usually is baffled).
NB - pet health and safety - pugs should be excluded when arc welding

After that, I ground it down smooth on the belt sander.
Then came a LOT of polishing. This was done on the random orbit sander starting with 120 grit and eventually going down to 240 grit. The handle shown here is not the final handle. It is just a temporary one used to hold the metal more safely.

Making a handle from foraged wood (about 2 hours)

This is a log scavenged from woods on the Chilterns. It is one of many logs left lying about after foresters had been thinning out ash trees. Ash trees self-seed really successfully so there were lots to be found. This was strapped to the back of the bike and taken home.

Ash is also a traditional wood used for tool handles because it is tough and shock-resistant and doesn't split. This log had been lying about for about a year when I retrieved it and I left it in my shed for another year or so before it was used, so it was more or less seasoned. A bit green, but ash doesn't split easily, so that was OK.

Ash is a really easy wood to work and has quite a nice grain. I also cut the handle out at a slight diagonal so the grain would be more prominent.

The log was roughed square with a power plane and hand planes, then this beautiful draw knife was used to start to form the final shape. This was done by eye until roughly the main shape

Then it was more finely carved using these two hand made chisels. The one on the left is a low profile gouge that is useful for carving curves. It is one I have modified from a flat standard bench chisel. The one on the right is a convex edged flat chisel that I invented. It is made from an old file. (files use the same high carbon steel as chisels and are easy to get hold of, for virtually nothing.)

I normally use it to do stop cuts when woodcarving. This is to match the curve of the concave inside of the blade of a gouge. In this case the slightly pointed corners also allow you to get into little corners to trim off subtle amounts of wood when shaping.

After carving the basic handle former, the fine finish is done back on the belt sander. This will file down wood even faster than metal. In this shot you can see my carving mallet, that used to be a wooden lawnmover roller. It's super heavy, lignum vitae I think. The handle I carved from a piece of beech.

Once the handle was almost finished, it was time to cut a slot for the handle. I didn't start final shaping until the blade was in place, so that the handle and blade merge into one seamless join in the handle.

Here it is before riveting and final shaping. You can see the handle is not yet fully formed and the blade tang is wider than it ends up.

Riveting the handle to blade (no time at all)

The handle rivet was simply a small coach bolt found in the road. Using a coach bolt is handy as its square shank end locks it in place in the wooden handle.

The blade was inserted into the handle slot and drilled in place to align the holes. Then using the mini anvil on this metalworking vice, I riveted the two together by inserting the bolt through and hammering the threaded end into a rivet head.

...using this lovely heavy lump hammer

Finishing (about 2 and a half hours)

As the slice was now in one piece, to finish off the sanding meant holding the blade. I prefer not to use gloves for finer control, but the flipside of that is you do get a few nicks when the blade judders. Occasional you sand your knuckles too. This is normal. You just develop quick reactions to pull your hand back and/or drop things in a hurry if you need to.

Here is the almost finished handle, post-sanding, but pre-cleaning of all the blood!

Cleaned up, the handle looks like this. The rivet has been sanded flush with the handle and the blade edges honed back to the wood.

Although gloves off is better, when fine polishing the metal blade, the friction makes it super hot, so gloves are unavoidable unless you want to burn off your fingerprints (tip - best avoided)

After fine grinding, the blade edge was honed smooth and sharp with an Arkansas stone. This is a super-fine, super-hard natural stone that I normally use to sharpen chisels.

After a lot of polishing on the orbital sander, the final polishing of the blade (both its flat and its edge) is done on a leather strop impregnated with emery paste (super fine grit in a waxy paste). This is the stuff that barbers use on their long leather strops to hone cut-throat razors.